- The Washington Times - Wednesday, November 20, 2002

Area residents who strained to see shooting stars from the recent Leonid meteor shower may not have realized it, but those streaks of light signify a constant threat from outer space. Since its formation, the Earth has been bombarded by streams of comets and asteroids. Most of them (like the cometary debris that produces the Leonids) burn up in the atmosphere, but larger-sized objects can impact with enough energy to destroy cities, countries, and even civilizations.

Since 1994, NASA scientists have been surveying and cataloguing the civilization-killing (greater or equal to 1 kilometer in diameter in size) near-Earth objects (NEOs). There are believed to be between 900 and 1,300 such objects, 90 percent of which should be identified by 2008.

However, the real danger might lie in the smaller NEOs. They're much smaller (between 200 and 500 meters in diameter), far harder to detect and far more numerous (estimated at 50,000). One of those objects could devastate a city, a state, or, in the case of an NEO strike in Tunguska, Siberia, in 1908 which went off with a force of about 10 megatons devastating 2,000 or so square kilometers of Siberian forest. In this year alone, there were at least three near-misses by such objects.

Notwithstanding such close calls, it's not completely clear how great a threat such objects pose. Estimates of the occurrence of Tunguska-sized events range from 200 to 1,000-plus years, NEO explosions in the five kiloton range are thought to occur about once a year.

Although mostly harmless, atmospheric detonations have the potential to set off even larger ones. Last June, with the governments of India and Pakistan on hair-trigger alert, a Hiroshima-sized NEO explosion occurred over the Mediterranean. Had it detonated over Kashmir, it may have been enough to start a war. That threat seems likely to become greater with time, as more and more nations join the nuclear club.

So what should be done? That question was discussed last month at a hearing into the matter at the House Subcommittee on Space and Aeronautics, led by chairman Rep. Dana Rohrabacher. While the Spaceguard program seems to be on track, another coordinated, cohesive federal program should be considered to catalogue the smaller NEOs, even if it means adding a digit or two to the budget deficit. At some point, scientists and engineers (other than Bruce Willis and Ben Affleck) will also figure out how to divert those NEOs that are found to be on a collision course with the Earth.

In testimony to the subcommittee, David Morrison, a senior scientist at NASA's Ames Research Center, pointed out that searching for NEOs is somewhat akin to buying a fire-insurance policy. Given the potential consequences, it seems wise to keep a wary eye on the skies.

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